1. Field of the Invention
The present invention relates to a stationary induction electric apparatus such as a transformer, an inductive reactance device, which is constituted by fitting windings around a transformer core wound from stripes of an amorphous magnetic alloy, and a method for manufacturing the stationary induction electric apparatus.
2. Description of the Related Art
Recently, amorphous magnetic alloys are paid attention as core materials because of low magnetic loss, and methods for manufacturing distribution transformers using a strip of an amorphous magnetic alloy have been studied.
Conventionally, cores for distribution transformers are made using silicon iron strips. According to a conventional manufacturing method, laminations each of which is comprised of plural silicon iron strip elements having been cut so as to have a length slightly larger than that of one turn are prepared and bent into a rectangular configuration. Then, plural laminations are packaged into a lamination block by abutting the ends of each of laminations stepwise. Furthermore, plural lamination blocks are built into a core. This type of core is called a core of one turn cut.
Upon manufacturing the core of one turn cut type, a wound silicon iron strip is cut by a length slightly longer than that of one turn while unwinding the wound strip. The cut strip elements are wound successively so as to form a circular core by staggering the joint position thereof to that of the foregoing one. The core thus formed is shaped into a rectangular configuration, and thereafter, it is annealed. Then, the core is opened once to fit windings therearound, and thereafter, the core is closed by jointing respective joints to build into a transformer.
An applicability of this method for manufacturing cores using an amorphous magnetic strip was studied at first. However, the amorphous magnetic strip is difficult to handle with since it has a thickness of about 25 .mu.ms which demands a laborsome and inefficient cutting operation.
In order to solve these problems, there has been proposed a method, wherein lamination units are formed by laminating plural strip elements (ten to several tens elements), and a core is formed using plural lamination units. According to this method, plural lamination units are stacked, and the stacked units are wound to form a lamination block by over lapping both ends of each of the units shifted with each other in stair step fashion. Then, plural lamination blocks thus formed are built to a core having a predetermined thickness.
After the core stacked to have a predetermined thickness is shaped into a rectangular shape with positioning an overlapping joint portion on one side of a yoke portion, it is annealed in a magnetic field. This annealing in the magnetic field can recover the original magnetic characteristics from the state that it is lowered due to a strain caused in the process for manufacturing the core. Thereafter, the overlapping joint portion of the core is opened once, windings are inserted into the leg portion of the core, and the overlapping joint portion of the core is closed again. Then, the interlinkage connection between the magnetic circuit and the conductive circuit is completed, resulting in that the stationary induction electric apparatus has its fundamental functions such as a voltage transformer, an inductive reactance device.
When the lamination unit having a proper thickness comprised of stacked strips is handled as if it is a sheet of magnetic steel, the working efficiency can be improved. However, since the lamination unit is constituted only by overlapping the strips, the mechanical characteristic of the strips does not vary when the strips are constituted as a lamination unit. Therefore, the hardness of the lamination unit is relatively low since the strip is extremely thin, and it is difficult to handle it since the strip becomes easily breakable after it is annealed in the magnetic field. Therefore, upon assembling the stationary induction electric apparatus, a reinforcement member is required in order to hold the core mechanically so as to maintain the shape thereof when it has been completely shaped.
According to a method proposed in the Japanese utility model application No. 63-121106 by the present applicant, the inner and outer peripheral surfaces can be easily maintained in a predetermined shaped configuration, and pieces of strip can be prevented from being released from a portion covered by the reinforcement member.
Since the strip after being annealed in the magnetic field is easily breakable as described above, it is necessary to pay attention to the assembling process particularly upon inserting the windings into the core. However, even though the strip is handled carefully, the strip can not be prevented from being broken, and it is difficult to prevent the broken pieces thereof from generating. Further, it may be impossible to prevent the broken pieces from generating even after the stationary induction electric apparatus has been manufactured. In order to solve these problems, a method for preventing the broken pieces of strip from coming out by winding insulating sheets on the outer surface of the core has been proposed.
According to the above method proposed in the Japanese utility model application No. 63-18450 by the present applicant, the insulating sheets can be wound on the core efficiently, and the core can be mechanically held by the insulating sheets.
Therefore, in the stationary induction electric apparatus using the strips as the core, it is necessary to reinforce the apparatus mechanically in order to maintain the core in the predetermined shaped configuration and prevent a stress from being applied to the core, and also it is necessary to prevent the broken pieces of strip from generating. According to the method proposed in the Japanese utility model application No. 63-121106, the core can be protected mechanically, however, a procedure required for preventing a stress from being applied to the core and preventing the strip from being broken upon mounting the reinforcement member on the core is not disclosed in the above application.
According to the method proposed in the Japanese utility model application No. 63-18450, the insulating sheets can be wound on the core efficiently, however, the core can not be protected enough since the insulating sheets themselves have not a high hardness.